Transmission equipped with reverse mechanism

ABSTRACT

A transmission having a reverse mechanism for use in an automotive vehicle which includes a forward shift drum both ends of which are rotatably supported by an engine case, and a reverse shift drum concentrically arranged with the forward shift drum and relatively rotatably fitted to the peripheral surface of the forward shift drum. This transmission comprises a first rotation positioning mechanism provided on one end portion of the foward shift drum and adapted to regulate a rotary position of the drum, and a second rotation positioning mechanism provided on the reverse shift drum at an end portion thereof opposite to the one end portion and adapted to regulate a rotary position of the reverse shift drum. These first and second rotation positioning mechanisms are disposed at the outer side of the engine case respectively.

BACKGROUND OF THE INVENTION

This invention relates to a transmission for use in an automotivevehicle, and more particularly to a transmission equipped with a reversemechanism.

In a conventional transmission equipped with a reverse mechanism for usein a three-wheeled or four-wheeled buggy car, etc., a forward shift drumrotated by a first operating element and a reverse shift drum rotated bya second operating element are separately supported within thetransmission. Upon rotation of each of these forward and reverse shiftdrums, shift forks engaged in lead grooves in the outer peripheralsurface of the drums shift, so that forward and reverse gears arebrought into driving engagement with a drive shaft by means of shiftersintegrally mounted to the shift forks.

However, a transmission having a forward and a reverse shift drumsseparately supported therein is increased in size. In view of theforegoing, the present assignee has proposed in its U.S. patentapplication Ser. No. 946,359 filed on Dec. 14, 1986, now U.S. Pat. No.4,713,979 that the forward shift drum and the reverse shift drum areconcentrically overlapped with each other in order to reduce the size ofthe transmission.

However, each of the shift drums is required to be provided with arotation positioning mechanism in order to regulate the rotary positionfor moving a predetermined shift fork. Accordingly, in the case theforward and the backward shift drums are overlapped, it becomes aproblem how and where to provide these rotation positioning mechanismsto the respective shift drums. Furthermore, it is desirable that theserotation positioning mechanisms are provided in such a fashion as tofacilitate a maintenance.

SUMMARY OF THE INVENTION

The present invention is directed to an improvement of a transmissionequipped with a reverse mechanism comprising a forward shift drumrotatably supported at both ends thereof by an engine case, and areverse shift drum concentrically arranged with the forward shift drumand relatively rotatably fitted on the peripheral surface of the forwardshift drum. The transmission equipped with a reverse mechanism accordingto the present invention includes a rotation positioning mechanismmounted on one end portion of the forward shift drum for regulating arotary position of the drum, and a rotation positioning mechanismmounted on the reverse shift drum at an end portion thereof opposite tosaid one end portion for regulating a rotary position of the reverseshift drum. These rotation positioning mechanism are provided at theouter side of the engine case, respectively.

According to the present invention, the rotation positioning mechanismsof the respective shift drums are mounted on the opposite ends so as notto interfere with each other, and these rotation positioning mechanismsare provided at the outer side of the engine case. Accordingly, uponmaintenance, the engine case is not required to be separated apart andopened. Instead, it is sufficient that a cover is simply removed.Accordingly, the maintaining performance is enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a sectional view of an important portion of a transmissionaccording to the present invention;

FIG. 2 is an enlarged perspective view of a shift drum portion;

FIG. 3 is a fragmentary perspective view of a rotation positioningmechanism of a reverse shift drum;

FIG. 4 is a front view of the rotation positioning mechanism of thereverse shift drum; and

FIG. 5 is a front view of a part of a rotation positioning mechanism ofa forward shift drum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described with reference to theillustrated embodiments. FIG. 1 is a sectional view of an importantportion of a transmission according to the present invention. A crankcase 1 (engine case) is provied. A forward shift drum 2 is rotatablycarried by bearings 3 and 4 which are mounted on both sides of the crankcase 1. Upon rotation of a forward shift spindle 5 disposed parallel tothe forward shift drum 2, the drum 2 is rotated by a lever 6 secured tothe spindle 5 and a connecting member 7 secured to the forward shiftdrum 2 and engaged in an elongated hole formed in the lever 6 in theradial direction thereof. Between the connecting member 7 and theforward shift drum 2, a rotation positioning member 8 which constitutesa rotation positioning mechanism of the forward shift drum 2 as will bedescribed hereinafter, is interposed. The connecting member 7 and therotation positioning member 8 are secured to the forward shift drum 2.The rotation positioning member 8 is disposed at the outer side of thebearing 3, i.e., the outer side of the crank case 1.

At the right side of the forward shift drum 2, a reverse shift drum 9 isdisposed coaxial with the drum 2. The reverse drum 9 is relativelyrotatably fitted to the forward shift drum 2 with a ball bearing 11 anda needle bearing 10 interposed between the outer peripheral surface ofthe forward shift drum 2 and the inner peripheral surface of the reverseshift drum 9. The ball bearing 11 is prevented from moving in the axialdirection by an inner race thereof being held between a step portion 12provided on the forward shift drum 2 and a set ring 13 fitted in agroove formed in the forward shift drum 2. The position of the reverseshift drum 9 in the axial direction is established with respect to theforward shift drum 2 by an outer race of the ball bearing 11 fastened tothe reverse shift drum 9 through a bearing holder 14 fixed to an endface of the reverse shift drum 9 by a bolt 15. An outer peripheralportion of the reverse shift drum 9 is formed with a sector gear portion16 integrally. A sector gear 17 meshes with the gear portion 16. Thesector gear 17 is secured to a reverse shift spindle 18 disposed inparallel with the reverse shift drum 9. Upon rotation of the reverseshift spindle 18 by a pedal (not shown, second operating element), thereverse shift drum 9 is rotated through the sector gear 17 and the gearportion 16.

The forward shift drum 2 and the reverse shift drum 9 are formed intheir overlapping portions respectively with lead grooves 21 and 22 (seeFIG. 2) crossing with each other, the grooves 21 and 22 being adapted tomove a shift fork 19 in the axial direction (A--B direction) of theshift drums 2 and 9 by guiding a pin 20 which is integral with the shiftfork 19. The lead groove 21 formed in the forward shift drum 2 has anupper end 21b of FIG. 2 inclined towards the right in the figure,whereas the lead groove 22 formed in the reverse shift drum 9 has anupper end 22b inclined in the opposite direction towards the left in thefigure. The lead groove 22 of the reverse shift drum 9 reaches the innersurface of the drum 9 so that the pin 20 can be pierced therethrough.Furthermore, the lead grooves 21 and 22 are provided at portions wherethe pin 20 is present when in a neutral position, with relief grooves21a and 22a projecting sidewards therefrom.

The shift fork 19 is slidably supported by a shift fork supporting shaft23 disposed in parallel with the shift drums 2 and 9 for sliding in theaxial direction or A--B direction. The opposite end portion of the shiftfork 19 to the pin 20 is engaged with a shifter 25 which is splinefitted to a drive shaft 24. The movement of the shift fork 19 in the Adirection causes the shifter 25 to move in the A direction to be engagedwith a low gear 26. The low gear 26 is loosely fitted to the drive shaft24. When the low gear 26 is engaged with the shifter 25, the gear 26 isconnected with the drive shaft 24 through the shifter 25 and isintegrally rotated together with the drive shaft 24. Similarly, when theshift fork 19 is moved in the B direction, a back gear 27 is connectedwith the drive shaft 24 through the shifter 25. In FIG. 2, the relativepositions of the shift drums 2 and 9 and the position of the pin 20 ofthe shift fork 19 when in the neutral position are illustrated. In orderto shift the gear from the foregoing state to LOW, after the clutch hasbeen brought to OFF-state, the forward shift spindle 5 is rotated torotate only the forward shift drum 2 in the C direction of FIG. 2. Then,the pin 20 is guided to the inclined section 21b at the front end of thelead groove 21 and is moved in the A direction. As a result, the shifter25 is brought to engagement with the low gear 26 and the power of thedrive shaft 24 is transmitted to the drive wheel side through the lowgear 26. At that time, even if the reverse shift drum 9 is attempted torotate by operating the reverse operating element, the reverse shiftdrum 9 will not be rotated because the pin 20 is fitted to the reliefsection 22a of the lead groove 22 of the reverse shift drum 9 and a sidewall of the relief section 22a functions as a detent or stopper. Whenreversing, the reverse shift spindle 18 is operated to rotate thereverse shift drum 9 in the C direction from the neutral position shownin FIG. 2. Then, the pin 20 is guided to the inclined section 22b at thefront end of the lead groove 22 and is moved in the B direction. As aresult, the shifter 25 is brought to engagement with a back gear 27 andthe power of the drive shaft 24 is transmitted to the drive wheel sidethrough the back gear 27 and an idle gear not illustrated. At that time,since the pin 20 is brought to be fitted to the relief section 21a ofthe lead groove 21, the section 21a functions as a detent or stopper anda forward operation cannot be performed through the forward shift drum2. In order to perform a forward operation, the reverse shift drum 9must be rotated in the opposite direction and returned to its neutralposition.

The shift fork supporting shaft 23 also supports other shift forks 28and 29. These shift forks 28 and 29, as known, are engaged with leadgrooves 30 and 31 formed in the outer periphery of the forward shiftdrum 2, respectively. When the forward shift drum 2 is rotated in theopposite direction to the arrow C from the neutral position of FIG. 2,the shift forks 28 and 29 are separately moved in the A direction or Bdirection according to the rotary position and causes the respectivesecond to fifth gears on the drive shaft 24 to be connected to the driveshaft 24 in turn in the manner as the afore-mentioned shift fork 19.

The forward shift drum 2 and the reverse shift drum 9 are provided witha rotation positioning mechanism, respectively, in order to hold each ofthem in a rotary position corresponding to the neutral or desiredshifting stage. A rotation positioning mechanism 32 of the reverse shiftdrum 9 will be described first with reference to Figs. 1, 3, and 4. Therotation positioning mechanism 32, as is shown in FIG. 1, is connectedwith the right end of the reverse shift drum 9 and is provided at theouter side of the crank case 1. The reverse shift drum 9 has the bearingholder 14 secured to a right end face thereof by the bolt 15 asdescribed. The holder 14 has bosses 33, 33 projecting from an oppositeend face thereof opposite to the shift drum 9 at positions generallyopposite to each other on a diameter. The bearing 4 portion of the crankcase 1 for carrying the forward shift drum 2, is formed therearound witharcuate through holes 34,34. The bosses 33 are projected outwards of thecrank case 1 piercing through these through holes 34. Upon rotation ofthe reverse shift drum 9, the bosses 33 are moved along the throughholes 34. A relief section 35 is expanded outwards, the inner sidethereof being depressed. Since the head portion of the bolt 15 is restedin the depressed portion, the bolt 15 can be freely moved according torotation of the reverse shift drum 9. A positioning member 36 is securedto end faces of the bosses 33 projecting outwards piercing through thethrough holes 34, by bolts 37. Accordingly, the positioning member 36 isintegrally rotated together with the reverse shift drum 9 at the outerside of the crank case 1. As is apparent from the foregoing description,the bearing holder 14 functions as a connecting member for connectingthe reverse shift drum 9 and the positioning member 36 together. Thepositioning member 36 is formed on the outer peripheral surface thereofat a position corresponding to the inclined section 22b at the tip endof the lead groove 22 of the reverse shift drum 9 with a reversepositioning portion 38 which is arcuately depressed, and at the neutralposition corresponding to the relief section 22 a of the lead groove 22with a neutral positioning portion 39 which is likewise arcuatelydepressed. Adjacent to the positioning member 36, a positioning arm 40is swingably attached to the crank case 1 by a pivot shaft 41. Thepositioning arm 40 has a roller 42 rotatably supported on the tip endthereof, the roller 42 being engagable with the reverse positioningportion 38 or the neutral positioning portion 39. The positioning arm 40is energized by a spring 43 to urge the roller 42 against thepositioning portions 38 and 39. Accordingly, the rotary position of thereverse shift drum 9 is regulated to a reverse position where the roller42 is engaged with the reverse positioning portion 38, or a neutralposition where the roller 42 is engaged with the neutral positioningportion 39, and is held in either one of the above-mentioned positionsunless a turning force overcoming the spring 43 is incurred by thereverse shift spindle 18 and will not occupy an intermediate position.The crank case 1 has a reverse lock 44 swingably attached thereto. Thereverse lock 44, when the reverse shift drum 9 is in the neutralposition, is in engagement with a cut-out portion 45 of the positioningmember 36 as shown by a chain line of FIG. 4 so as to lock the rotationof the reverse shift drum 9. The reverse lock 44 is linked to a lever ona steering wheel and is moved to a position shown by a solid line tounlock the reverse shift drum 9 when the lever is manipulated.Accordingly, when reversing, the lever on the steering wheel must bemanipulated first to unlock the reverse shift drum 9. Therefore, even ifthe reverse shift spindle 18 should be unintendedly manipulated bymistake during the forwarding operation, the reverse shift drum 9 wouldnot be rotated to the reverse position.

The above-mentioned positioning member 36, positioning arm 40, reverselock 44, etc. are all disposed on the outer side of the crank case 1 andthe exteriors thereof are covered with a cover 46 which is mounted onthe crank case 1 (see FIG. 1). The cover 46 has a reverse indicatorswitch 47 attached thereto. A contacting piece 47a of the switch 47 isactuate by a reverse indicator rotor 48 secured to the positioningmember 36 when the reverse shift drum 9 has moved to the reversingposition, and the switch 47 is turned on. As a result, an indicatinglamp, for example, on a panel in front of the driver is lighted up toindicate that a reversing operation is undergoing.

A rotation positioning mechanism 49 of the forwarding shift drum 2comprises the aforementioned positioning member 8. The rotationpositioning member 8 is formed on the peripheral surface with a neutralpositioning portion 50, a second speed positioning portion 51, a thirdspeed positioning portion 52, etc., similar to the positioning portions38 and 39 of the positioning member 36 in turn as shown in FIG. 5, sothat a roller 54 rotatably supported on the tip end of a positioning arm53 which is pivotally attached to the crank case 1, may be engaged withthese positioning portions 50, 51, 52, etc. The positioning arm 53 isenergized counterclockwise in FIG. 5 by a spring 55. As the rotationpositioning member 8 is rotated and moved in the arrowed direction fromthe illustrated position according to the rotation of the forward shiftdrum 2, the roller 54 is caused to engage with the positioning portions50, 51, 52, etc. in turn so as to hold forward shift drum 2 in a rotaryposition corresponding to a desired shifting stage. The exterior of therotation positioning mechanism 49 is covered with a cover 56 (FIG. 1).

In the present embodiment, the forward shift drum 2 and the reverseshift drum 9 provided at the respective opposite end portions withrotation positioning mechanisms 49 and 32, are coaxially fittedoverlapping with each other. Accordingly, the transmission as a wholecan be made compact. Moreover, the rotation positioning mechanisms 49and 32 are all disposed at the outer side of the crank case 1.Accordingly, when these rotation positioning mechanisms and the reverselock 44, the reverse switch 47, etc. attached to the mechanisms are tobe maintained, the cover 46 or the cover 56 may be simply removed, andthe crank case 1 is not required to be disassembled to open the interiorthereof. Accordingly, the maintaining work is extremely easy.

Furthermore, in the present embodiment, the reverse shift drum 9 isfitted to the peripheral surface of the forward shift drum 2 by theneedle bearing 10 and the ball bearing 11, and the positioning of thereverse shift drum 9 in the axial direction is performed by holding theouter race of the ball bearing 11 between the reverse shift drum 9 andthe bearing holder 14, and no portion is present between the forwardshift drum 2 and the reverse shift drum 9, where a friction resistanceis produced by face contact. Accordingly, both of them can perform asmooth rotary motion independently.

What is claimed is:
 1. A transmission having a reverse mechanismincluding a forward shift drum both ends of which are rotatablysupported by an engine case, and a reverse shift drum concentricallyarranged with said forward shift drum and relatively rotatably fitted tothe peripheral surface of said forward shift drum, said transmissioncomprisinga first rotation positioning mechanism provided on one endportion of said forward shift drum for regulating a rotary position ofsaid forward shift drum; and a second rotation positioning mechanismprovided on said reverse shift drum at an end portion thereof oppositeto said one end portion for regulating a rotary position of said reverseshift drum; said first and second rotation positioning mechanisms beingdisposed at an outer side of said engine case, respectively.
 2. Thetransmission as claimed in claim 1, wherein an exterior of said rotationpositioning mechanisms is covered with a cover respectively.
 3. Thetransmission as claimed in claim 1, wherein said rotation positioningmechanism of said reverse shift drum comprisesa connecting membersecured to an end portion of said reverse shift drum and having a bossprojecting outwards of said engine case piercing through an arcuatethrough hole formed in the engine case; a positioning member secured toan external end of said boss and provided on peripheral surface thereofwith a depressed reverse positioning portion and a depressed neutralpositioning portion; and a positioning arm swingably mounted on saidengine case and selectively engaged with said reverse positioningportion and said neutral positioning portion.
 4. The transmission asclaimed in claim 3, wherein said rotation positioning mechanism of saidreverse shift drum includes a reverse lock adapted to lock saidpositioning member when said reverse shift drum is in the neutralposition.
 5. The transmission as claimed in claim 3, wherein saidreverse shift drum and said connecting member have an outer race of aball bearing held therebetween, and an inner race of said ball bearingis secured to said forward shift drum.